CONTACTOR CONSTRUCTION

Abstract: A liquid/liquid or solid/liquid contactor comprising a substantially hollow cylindrical outer shell, and a rotor assembly mounted for rotation within the interior of said shell, the rotor assembly including a plurality of axially spaced generally circular plates, the spacing between adjacent plates defining a compartment of the rotor, a peripheral clearance provided between the periphery of each said plate and the internal surface of said shell, characterised in that at least one elongate solids movement assisting bar is located between at least two adjacent plates at or near their periphery.

Description: CONTACTOR CONSTRUCTION This invention is concerned with a contactor construction. More particularly it is concerned with the construction of a liquid/liquid or solid/liquid mass trans¬ fer contactor, and such contactors are useful in large scale solvent extraction techniques and other similar mass trans¬ fer operations. One known form of liquid/liquid and solid/liquid contactor is the multi-compartmented cylindrical rotor contactor known as the Graesser Contactor, manufactured and sold by the Applicants. This known form of contactor which finds wide applications in solvent extraction and in other mass trans¬ fer operations is shown fully assembled in Figure 1, par¬ tially dismantled in Figure 2 and its method of operation is depicted schematically in Figure 3. The known Graesser Contactor, of the type illus¬ trated in Figures 1-3, works on what is termed in the art as ' a "raining bucket" principle enabling intimate mixing of a liquid feed and applied solvent over a plurality of theoret¬ ical stages of mass transfer but within a single apparatus. The Graesser Contactor shown in Figures l and 2 is a horizontal cylindrical machine having an outer shell 1, a centrally located spindle 2 connected via drive train 3 to a relatively low power motor 4. Because of the size and weight of the contactor it is conveniently mounted on rigid supports 5 forming part of a mounting platform. The outer shell is provided with a number of take-offs 6 either for removing liquid from intermediate stages within the contac¬ tor or which can be useful as gas vents, during a mass transfer operation. As shown in Figure 2, the rotor assembly 8 com¬ prises a pair of end plates 9 (only one of which is shown in this drawing) connected to a plurality of axially spaced cylindrical plates 10 between which are located "scoops" 11 - 2 - which serve to collect solid or liquid from the feedstock and cause this to be mixed with an applied solvent or other extraction medium. Accordingly a plurality of adjacent compartments are formed within the interior of the contac¬ tor, the first compartment of which is defined by the space between end plate 9 and its immediately adjacent cylindrical plate 10. The method of operation of the known Graesser Contactor is shown in simplified form in Figure 3. A liquid or liquid/solid feedstock enters feed inlet 7 and can be applied on a continuous basis to approximately fill one half of the volume of the interior of the contactor. The feed¬ stock when treated exits as raffinate at outlet 7a. A solvent (or other liquid) is applied at solvent inlet 6a and exits the contactor via outlet 6b containing the material extracted from the feedstock. The feedstock is designated 12 and the solvent designated 11, one compartment being defined by the space 13 between adjacent axially spaced plates 10. The scoops (not shown in Figure 3 but visible in Figure 2) cause a relatively gentle mixing as between feed¬ stock 12 and solvent 11 without excessive agitation, bub¬ bling or frothiness. Such is possible by use of a relative¬ ly low powered motor 4 to drive the spindle 2 and hence the rotor assembly 8. Graesser Contactors are established items of industrial hardware and have found considerable commercial application in the treatment/extraction of phenolic liquors and effluents, tar acid extractions from carbonisation distillates, extraction of products from aqueous reaction mixtures, desalination of organic reaction products by water washing, purification of herbicides and other similar ex¬ traction techniques useful in the chemical industry, water and effluent treatment, agricultural, food and pharmaceuti¬ cal industries. Such contactors with gentle (low rpm) mixing techniques have been used in separation techniques otherwise requiring distillation, evaporation, crystallisa- tion, zone refining and leaching processes. Early applications of the Graesser Contactor were in a liquid-liquid mode with the flows of both phases taking place in the interfacial gaps between the shell and the compartmental dividing plates. Whilst the upper phase is usually the solvent phase and the lower phase the solute phase examples exist of where the densities are reversed. Flow design is related to the pressure drop across each of the interfacial areas, and the summation of each of the pressure drops. Originally, the Graesser Contactor was used in extractions from slurries in the aqueous phase; or other denser phase. These slurries were passed entirely through the lower peripheral gap (spacing between rotor periphery and interior surface of cylindrical housing) - aided by eccentricity of the rotor to increase the lower gap at the expense of the upper. As the demands for greater percentages of solids in the slurry continued, and more difficult materials were used e.g. (A) Larger size particles (Gravels-Metals) , (B) More Cohesive materials (Clays) , and (C) More entwining material (vegetable matter) , modifications were needed to the assembly, to handle the higher solids material more effectively. This was done by piercing the compartmental divid¬ ing plates alternately behind each pair of buckets (scoops) - thus passing solids compartment, to. compartment, without. allowing by-passing since the material could only pass one dividing plate without being lifted and dropped through the other phase. This system has been used, but there remains room for further improvements. • However, the Graesser Contactor is increasingly used for environmental clean-ups, and for highly cohesive industrial materials often bound together by bitumens. All this has lead to a need for a contactor of the Graesser type having a 'drive mechanism' for solids movement but which nevertheless minimises disturbance of the solvent phase. Other desirable features of such a 'drive mechanism' include adjustability to reduction from the maximum drive available and it should preferably be proportional to the speed of revolution of the rotor. According to this invention we provide a liquid/liquid or solid/liquid contactor comprising a substantially hollow cylindrical outer shell, and a rotor assembly mounted for rotation within the interior of said shell, the rotor assembly including a plurality of axially spaced generally circular plates, the spacing between adjacent plates defining a compartment of the rotor, a peripheral clearance provided between the periphery of each said plate and the internal surface of said shell, characterised in that at least one elongate solids movement assisting bar is located between at least two adjacent plates at or near their periphery. It is preferred to use one or even several assisting bars extending from one end plate of the rotor to the other end plate, thus allowing more effective, solids movement whilst permitting the solid movement to be proportional to the rotor speed. The number of assisting bars can be increased or decreased if they are removable and the inter-compartmental partitions e.g. plates'as specified above may have slots or similar notches cut in them, at or near their periphery, into which the bars can be placed or withdrawn. The bars can extend diagonally across the or each compartment defined by the rotor assembly and the shell. For example six "sets" of diagnonal bars can be used although a practical maximum might be ten "sets" wherein a "set" is one bar which extends between the two end plates of a rotor, but which is itself made up of a number of end-linked, smaller assisting bars having protuberances which engage notches in the plates at the ends of the smaller bars. The or each assisting bar can be constructed of metal, preferably corrosion resistant metal such as stainless steel or the like, but it could be constructed of strong, essentially inert plastics material such as PTFE, carbon fibre, or polypropylene. It has been found convenient for the bars to be constructed of metal, allowing the provision of a series of connected metal strips or blades placed in suitably sized notches located at the peripheral surface of dividing plates of the rotor assembly. The bar or bars may be in the form of a metal strip or helically wound blade extending across a plurality of compartments. A number of assisting bars can be employed within the interior of the contactor, in radial¬ ly-spaced location. A continuous assisting bar can be comprised of a series of end-linked smaller bars, wherein one such smaller bar extends across the two plates defining between them a compartment. Best results are likely to be obtained with a solids/liquid rotor, optionally including piercings. In order that the invention including further preferred and optional features may be illustrated, more easily appreciated, and readily carried into effect, embodi¬ ments of the invention are now described with reference to the accompanying drawings by way of non-limiting example only and wherein: Figs. 1-3 show a conventional form of contactor and have already been described, Figure 4 shows an internal view of a modified contactor according to the invention, Figure 5 is a side elevation of the rotor assembly shown in Figure 4, Figs 5a - 5c show enlarged details of the connec¬ tion between assisting bars respectively along the lines f- f, e-e and d-d noted on Figure 5, Figure 6 shows an end elevation of one plate member, such as an end plate used in the rotor assembly, and Figs 6a - 6c show enlarged details of assisting bars located in peripheral plate notches along the lines f- f, e-e and d-d shown in Figure 5. Referring to the drawings Figures 1-3 have already been described for purposes of background information and for identifying one preferred form of contactor which may be modifie by use of one or more assisting bars, and so pro¬ vide a contactor capable of better solids movement according to the present invention. Figure 4 shows an isometric view of part of the interior section of a contactor, modified by inclusion of a solids movement assisting bar 15. The bar 15 is comprised of a series of inter-connected smaller such bars where individual bars extend between a pair of adjacent plates 10 (and/or 9,10) of the rotor assembly 8. The rotor assembly shown includes an end plate 9, and a series of adjacently spaced plates 10 which are joined by connecting rods 14. In practice the connecting rods 14 may be attached to bucket-like scoops as in a conventional Graesser Contactor. Each of the plates 9, 10 has a series of radially spaced inwardly directed, peripherally located and radially spaced notches 16. The assisting bar is in the form of a helically wound metal blade. A number of smaller bars are welded together at their abutting ends, to form the helical blade 15. Each smaller bar has a protuberance at its end (15e - see Figs 6a-c) which fit into co-operating notches 16. Figure 5 shows the arrangement, in elevation, of the rotor assembly where a plurality of solids movement assisting bars 15 are deployed. Each compartment of the rotor assembly being defined by adjacent plates 10, or by an end plate 9 and its adjacent plate 10, includes a plural¬ ity of peripherally spaced assisting bars, but the bars can be removed to reduce their number. Joining locations, 15a, 15b and 15c (Figure 5) are shown in Figures 5a to 5c. Figure 5b shows a detail of the optionally welded joint designated 15b between bars 15 at the notch 16 along the line e-e shown in Figure 5. Joint 15a between bars 15, shown in Figure 5a is a detail of the arrangement shown in Figure 5a. Similarly, the joint 15c is shown in Figure 5c. It will be appreciated that the includ¬ ed angle between two bars may be varied. Whereas Figures 5a and 5c show an included angle of the order 36°, the included angle in the arrangement shown in Figure 5b can be of the order 72°, for example. Figure 6 shows a plate 10, which could be an end plate 9, having ten equi-distantly spaced, inwardly directed rectangular notches 16, some of which have been designated 16A, 16B, 16C; 16D and 16E. In one embodiment,the abutting projections 15e (see Figs 6a-6c) can be located in notches of adjacent plates designated 16A to 16C whereas in another embodiment of a contactor, for exam¬ ple the type shown in Figure 6c, incorporating a metal strip I5d of thicker section than the element to which it is joined, may extend from notch 16A in the first plate, there¬ after to notch 16B, to notch 16C, to notch 16D and then to notch 16E before reaching another notch designated 16A. Finally Figures 6a-6c show one way of connecting bars 15 and locating their projecting protrusions 15e within a notch 16 of a plate 10 or end plate 9. The bars might be welded or only temporarily fastened together at the protru¬ sions 15e and, if necessary or desirable, in appropriate position within the notch 16. In use, the assisting bar or bars may extend across compartments of the rotor assembly whilst still leaving an operating clearance between the outermost periph¬ eral surface of the or each assisting bar and the interior surface of the shell of the contactor. Such an arrangement can improve control of solids flow. The bars can be fabricated from readily available materials and can be affixed to appropriate plates of the rotor assembly. Considerable performance enhancements may be achieved with a modified contactor according to this invention.

Claims: CLAIMS 1. A liquid/liquid or solid/liquid contactor comprising a substantially hollow cylindrical outer shell, and a rotor assembly mounted for rotation within the interior of said shell, the rotor assembly including a plurality of axially spaced generally circular plates, the spacing between adjacent plates defining a compartment of the rotor, a peripheral clearance provided between the periphery of each said plate and the internal surface of said shell, characterised in that at least one elongate solids movement assisting bar is located between at least two adjacent plates at or near their periphery. 2. A contactor as claimed in claim 1 comprising one or more assisting bars which extend from one end plate of the rotor to its other end plate. 3. A contactor as claimed in either preceding claim wherein the or each assisting bar is removable. 4. A contactor as claimed in any preceding claim wherein one or more plates has notches or similar slots at or near their periphery. 5. A contactor as claimed in any preceding claim wherein the or each assisting bar extends at an acute angle with respect to the faces of the plates between which it, or they, extend(s). 6. A contactor as claimed in any preceding claim comprising one or more assisting bars fabricated as a series of smaller, end-linked assisting bars, with protuberances which engage said plates. 7. A contactor as claimed in claim 6 comprising 6-10 series of such assisting bars. 8. A contactor as claimed in any preceding claim wherein the or each assisting bar is helically coiled or wound about the external periphery of the rotor, across a plurality of compartments. 9. A contactor as claimed in any preceding claim wherein a plurality of said plates have inwardly directed and radially spaced grooves or notches capable of removably receiving an assisting bar therein or at least an end part or a protuberance thereof. 10. A rotor assembly useful in a contactor as claimed in any preceding claim which comprises, in combination, the rotor assembly as defined in claim 1 and affixed thereto one or more solids movement assisting bars as defined in any one of claims 1 to 9. 11. Use of a contactor as claimed in any one of claims 1 to 9 in a liquid/liquid or liquid/solid extraction process. 12. Use as claimed in claim 11 in a liquid/solid extraction process wherein the composition to be extracted contains one or more of the following: gravels, metals, clay, vegetable matter and/or bitumen.

Inventors: ROBINSON LEE FISHER, ROBINSON, LEE, FISHER
Applicants: GRAESSER CONTACTORS LTD, ROBINSON LEE FISHER, GRAESSER CONTACTORS LTD., ROBINSON, LEE, FISHER
Application year: 1994
Main classification: B01D11
IPC codes: B01D11